The Torsional Vibrometer with Long Natural Period
Teruo Takagami, Yasuo JIMBO, Masaharu Takano · Journal of the Japan Society of Precision Engineering · 1971
A torsional vibrometer with long natural period has been produced. The dimensions are 94φ×95 mm, weight 825 g, and the natural period 19 sec. A size 72φ×37 mm empty cylinder which has a apparement specific weight less than unity, rotates around a vertical axis. The case of the rotor is filled with a mixture of two kinds of oil adjusted to have the same specific weight as the rotor. Thus the weight of the rotor is supported by the buoyancy of the oil and the load of pivot bearings becomes very light. A hair spring of a clock is used as a restoring spring. The inner terminal of the hair spring is attached to the axis of the rotor and the outer termial is attatched to a fixture of the case. The position of the fixture can be adjusted to regulate the neutral position of the rotor. The movement of the rotor is detected by the change of electric capacity. Six pairs of electrodes are attached to the rotor and the case. It's sensitivity is 4.6 pF/rad. Frequency characteristics of an electric circuit can be changed by changing a capacity or a resistance in the circuit. This adjustable electric circuit compensaites the change of frequency characteristics of the movement of the rotor by temperature.